The genus Clostridium consists of gram-positive, anaerobic, spore-forming bacilli. The natural habitat of these organisms is the environment and the intestinal tracts of humans and other animals. Despite the identification of approximately 100 species of Clostridium, only a small number have been recognized as etiologic agents of medical and veterinary importance. Nonetheless, these species are associated with serious diseases, including botulism, tetanus, anaerobic cellulitis, gas gangrene, bacteremia, pseudomembranous colitis, and clostridial gastroenteritis.
Clostridium perfringens is the etiological agent for numerous clostridial diseases found in economically valuable domestic animals. Necrotic enteritis (NE) is one example of a clostridial enteric disease caused by C. perfringens. Necrotic enteritis leads to the development of necrotic lesions in the gut wall resulting in morbidity and mortality of poultry. It is also a multifactoral disease with complex and partly unknown epidemiology and pathogenesis (Kaldhusdal, 1999). The bacterium, C. perfringens is commonly found in the gastrointestinal tract of poultry (Tschirdewahn et al., 1991), the occurrence of necrotic enteritis, however, is sporadic (Cowen et al., 1987). Nevertheless, feed contaminated with C. perfringens has been implicated in outbreaks of necrotic enteritis in chickens (Kaldhusdal, 1999). Studies have also shown that healthy chickens have a relatively low number of C. perfringens in their gastrointestinal tracts, while an increase in the concentration of the bacteria can result in a necrotic enteritis condition (Craven et al., 1999).
Clinical necrotic enteritis is thought to occur when C. perfringens proliferates to high numbers in the small intestine and produces extracellular toxins that damage the intestine. The major toxin believed to be involved is the alpha-toxin, but its precise role in the disease process is not completely understood. The alpha-toxin is a secreted zinc-metalloenzyme which has both phospholipase C and sphingomyelinase activity and is the major toxin involved in the pathogenesis of human gas gangrene (Awad, et al., 1995; Songer, 1997). All five toxin types of C. perfringens (A to E) carry and express the alpha-toxin structural gene, plc.
To date, no other toxin had been identified as an essential virulence factor in necrotic enteritis.